[R] Unexpected result of names<-

Hong Ooi Hong.Ooi at iag.com.au
Wed Nov 16 02:01:38 CET 2005


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I came across some rather unexpected behaviour the other day with
assigning names and lists. Here's an example.

> z <- list(aaa=1, bbb=2)
> z
[1] 1

[1] 2

Note that z has members named "aaa" and "bbb". Now:

> names(z$a) <- "X"
> z
[1] 1

[1] 2


I would have expected that trying to name z$a would either give an error
(because z doesn't have an element "a") or would cause z$aaa to be
modified (due to partial name matching).  I didn't expect that a new
list member would be created.

I've checked that this is consistent across SPlus 2000, SPlus 7, and R
2.2 for Windows. Can someone give an explanation for why this is

Hong Ooi
Senior Research Analyst, IAG Limited
388 George St, Sydney NSW 2000
(02) 9292 1566


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